Make IterableDataset dataloader.__len__ warning clearer (#41175)
Summary:
Based on discussion with jlucier (https://github.com/pytorch/pytorch/pull/38925#issuecomment-655859195) . `batch_size` change isn't made because data loader only has the notion of `batch_sampler`, not batch size. If `batch_size` dependent sharding is needed, users can still access it from their own code.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/41175
Differential Revision: D22456525
Pulled By: zou3519
fbshipit-source-id: 5281fcf14807f219de06e32107d5fe7d5b6a8623
